Modelling and quantitative analyses of WR spectra:
recent progress and results

W.-R. Hamann, L. Koesterke and G. Gräfener

Universität Potsdam, Institut für Physik, Lehrstuhl Astrophysik Postfach 601553, D-14415 Potsdam, Germany

The quantitative analysis of Wolf-Rayet type spectra requires non-LTE-models for expanding atmospheres which have been developed in the last decade. Idealizing assumptions of the so-called standard model are spherical symmetry, homogeneity and stationarity. While the first generations of models were restricted to simple atoms (helium, hydrogen), we now apply more advanced calculations which account for complex model atoms (nitrogen, carbon, oxygen). The re-analysis of the Galactic WN sample from the nitrogen lines led to a substantial revision of the stellar parameters, as far as the WNE-w subclass is concerned.
Wind inhomogeneity ("clumping") has been accounted for in a first-order approximation. The degree of clumping is derived from the electron-scattering wings of strong lines. With clumped models, considerably lower mass-loss rates (by a factor two or more) are obtained, while other empirical parameters are not affected significantly.
An overview is given about the fundamental parameters of Wolf-Rayet stars as obtained from spectral analyses, including new results on WN stars in the LMC.

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